Smokeless powder manufacture



March s, 1966 R. G. GUENTER 3,239,583

SMOKELESS POWDER MANUFACTURE Filed June 8, 1946 Fl G .2

RICHARD GGUENTER INVENTOR.

AGENT United States Patent O 3,239,583 SMOKELESS PDWDER MANUFACTURERichard G. Guenter, Kenvil, NJ., assignor, by mesne assignments, to theUnited States of America as represented by the Secretary of the ArmyFiled .lune 8, 1946, Ser. No. 675,435 Claims. (Cl. 264-3) This inventionrelates to the manufacture of cast propellents and, more particularly,to a large cast propellent and method of making same whereby faultilyprepared castings are detected and eliminated.

In the casting of large smokeless powder propellents -by the methodinvolving curing a mixture of casting powder, burning rate controlpowder, and nonvolatile plasticizers at elevated temperatures, it isessential that all components be uniformly distributed throughout toform a homogeneous casting. Local concentration of nonvolatileplasticizer, casting powder, or burning rate control powder, as well asentrapped air cause fluctuations during burning and can lead touncontrolled fast burning with high pressure development and evenrupture of the combustion chamber walls of jet-controlled devices inwhich such powders may be used.

Uniform distribution is diflicult to obtain, particularly when theburning rate control powder is in the form of granules comparable insize to the casting powder granules. Thus, when the powders are blendedand added to the casting container or mold, the denser burning ratecontrol particles tend to segregate. This tendency is increased when theblended powder granules and the liquid plasticizers are ladded to themold in successive increments and agitated in accordance with methodsheretofore used.

The tendency to segregation may be minimized by employing the improvedcasting methods disclosed in the copending application of Donald L.Black, Ser. No. 675,436, filed June 8, 1946, now Patent No. 3,205,286,which involves placing the blended powder in a mold, placing a weight ont-op of the powder and introducing the liquid plasticizers through anopening in the bottom of the mold. Nevertheless, it is possible thatthrough careless manipulation or for other reasons, segregation maysometimes occur, thus resulting in a faulty casting which should beeliminated.

Although -it is important that faulty castings be detectcd andeliminated, this has not been easily possible heretofore. Visual methodshave been generally unsatisfactory due to the diiiculty ofdistinguishing the individual components. Thus, where the burning ratecontrol powder is in the form of granules, the granules of castingpowder and of burning rate control powder are all .about the same size,shape, and color, making it diiiicult to pick up nonuniformities. Again,where the burning rate control powder is in the form of filaments orstrands, flaws in the finished casting, such as irregular placement ofthe filaments or introduction of an improper number of filaments, arenot easily detectable.

X-rays have been used to some extent to detect faulty castings but donot give satisfactory results in all cases. Furthermore, the use ofX-rays -is tedious, time con-suming, and expensive, and hence is notdesirable for these reasons.

Now, in accordance with the present invention, it has been found thatfaulty cast propellents may be detected and eliminated by a methodinvolving forming the powder components with distinctly differentcolors. Furthermore, it has been found that the novel cast propellentsof this invention have properties such that the homogeneity of thecasting may be determined by visual inspection.

In general, the powder components to be utilized com- Patented Mar. 8,1966 ICC prising a casting powder, a burning rate control powder, and acasting solvent, will have incorporated therewith materials which willimpart to the components distinctive colors. Alternatively, the powdercomponents may be coated with or otherwise treated by -suitablematerials to impart the desired distinctive colors. The casting powderand burning rate control powder are then mixed, ladded to a transparentcasting container, and the casting solvent introduced through an openingin the bottom. The container contents are then cured at elevatedtemperatures to form the cast propellent.

When the mixture of casting powder and burning rate control powder isadded to the casting container, the different colored granules of eachform a color pattern which gives a visual indication of the uniformityof distribution of the granules. Thus, a local concentration of granulesof one color is 4readily picked up and indicates that the distributionis faulty. The faulty mixture may thereupon be eliminated lat this stageof the process, thus saving the additional time, expense, and labornecessary to complete the casting of the charge. Visual indication isalso possible at subsequent points in the operation, such as after thecasting solvent is added, and after the charge is cast. In each case,the color pattern indicates the uniformity of distribution of the powdercomponents in the casting and facilitates detection and elimination offaulty castings. When r-ate control powder in the form of strands ofdistinctive color is utilized, examination of the ends of the castingreveals omission or nonuniform spacing of the strands.

The cast propellant in accordance with this invention is illustrated inthe accompaning drawing in which:

FIG. 1 is a View showing a cast propellant charge having the powdercomponents distributed uniformly therethrough, and

FIG. 2 is a view showing a faulty cast propellent charge having localconcentrations of rate control granules.

In a homogeneous casting as shown in FIG. 1, the different coloredparticles blend into a harm-onions pattern giving the effect ofuniformity. Local concentrations of one material emphasize theparticular color of that material in the locale of the concentration andare easily detected as shown in FIG. 2.

IIn accordance with the invention and to illustrate more particularlythe improved product and method of producing it, the following exampleis given:

Example Twenty-one castings were prepared using powder components asfollows:

Burning Casting Rate Casting Powder, Control Solvent, percent Powder,percent percent Nitroeellulose (13 15% N) 73. 5 25. 00 Nitroglycerin 20.0 6. 66 74. 0 Carbazole 1.5 1.05 0.5 Potassium perchlorate- 56. 00Carbon black 9.00 Diethyl phthalate 5. 0 2. 29 25. 5 Titanium dioxide 0.5 (added) `Both powders were granulated in the form of cylindersapproximately 0.034 inch diameter x 0.033 inch high and then blended inthe ratio of 1 part burning rate control powder to 4 par-ts castingpowder by tumbling for 20 minutes in a sweetie barrel. Thev 4blend wastransferred to a wooden hopper from which 3,540 g. was dischargedthrough an 0.75-inch opening directly into a transparent plasticcylindrical mold 4 inches inside diameter and 18 inches long. The moldwas vibrated by an air-operated vibrator (frequency 3,000 vibrations perminute, amplitude 0.03 inch) for about 1 minute in order to compact `thepowder.

The powder-filled mold was then examined to determine homogeneity. Sincethe titanium dioxide colored the casting powder granules white and thecarbon black colored the burning rate control powder granules black, anylack of uniformity in the distribution of the black granules through thewhite granules was clearly evident. When faulty distribution wasdetected, the contents of the mold were dumped back into the sweetiebarrel for .reblending and the mold refilled. Six molds were emptied andrefilled in prepar-ing the samples of twenty-one castings. Although someof the charges reblended might have burned entirely satisfactory incombustion tests, it is significant that the operator was dissatisfiedwith the degree of uniformity in the distribution of the black and whitegranules.

The mold was evacuated for 1 hour at a pressure of 4 mm. mercury toremove surface moisture from the powder, a 20-pound weight placed on topof the powder column, and 1,610 g. of casting solvent or plasticizermixture, which had been previously evacuated for 3 hours at a pressureof 3 mm. mercury to remove moisture and dissolved air, admitted into themold through 0.375 inch diameter tube at the rate of 270 g. per minute.When the liquid had displaced the air in the powder column and 'formed alayer about 0.1 inch above the column, the iiow of plasticizer wasstopped, the tube in the bottom of the mold closed off and disconnectedfrom the plasticizer reservoir, and the weight removed from the top ofthe column. The casting was cured for 40 hours at 60 C.

All castings were satisfactory in static burning tests at normaltemperature. Pressures were very uniform throughout each test.

In the preparation of cast propellants in accordance with thisinvention, the powder components, including the plasticizers, ifdesired, are given distinctively different colors. This may beaccomplished in any suitable manner and at any point in the processprior to mixing and introducing the powders into the casting container.Preferably, the powder components are colored by adding the desiredtinting agent to the powder ingredients during mixing or colloiding.Alternatively, the color may be added as a surface coating after thegranules have been dried. Other means will suggest themselves and arecontemplated as being within the scope of the invention.

The coloring ingredients may comprise any suitable materials whichimpart distinctive colors such as black, white, red, yellow, green,etc., to the powder components. Thus, dyestuifs or inorganic pigmentssuch as iron oxide, lead chromate, chromium oxide, titanium oxide, andzinc oxide or organic pigments such as para red, yellow lakes andphospho-tungstic greens are typical examples of suitable materials whichcan be used. In addition, many of the organic dyestuifs and othersimilar 'coloring agents may be used. Where it is desirable tolncorporate an opaquing agent in large-web propellents to prevent wormholing during combustion, the presence of such material need notinterfere with coloring of the granules, for it is possible to selectopaquing agents that in themselves impart the desired cont-rast to thepowder granules. Such a selection is illustrated by the example, wheretitanium dioxide was used in the casting powder and carbon black wasused in the burning rate control powder.

The coloring ingredient is added in comparatively minor amounts so asnot to substantially detract from the calorific value of the powder.Thus, from about 0.4% to about 0.6% by weight of the powder componenthas been found to give good results and is preferred. Such amounts arenot critical, however, and may be varied in accordance with particulardesires and usages as long as the desired distinctive colorcharacteristics are imparted to the powder.

Inspection for nonuniformity may be made at any point in the operationafter the powder has been added to the mold. However, the chances ofdetecting faulty grains and reusing the smokeless powder components aregreatest before the casting solvent has been added to the mold and henceit is preferred to make the principal inspection at this time. Alternateor additional inspections may be made after the casting solvent has beenadded and/or after the casting has been cured.

Inspection of the casting may be made in any suitable manner and withany suitable means by which nonuniformity in distribution of the powdercomponents may be determined. Since the naked eye is very sensitive tofaulty patterns, visual inspection is entirely adequate and ispreferred. However, it is within the scope of this invention to use suchldevices as photoelectric cells, or photometers specially adapted toindicate when the distribution of the powder components is faulty.

The powder components in accordance with this invention will comprise agranular casting powder, a burning rate control powder in the form `ofgranules, strands or filaments, and a casting solvent consistingessentially of a mixture of nonvolatile plasticizers. Composition andformulation of the powder components may be as set forth in the exampleor in accordance with principles well known in the art. As pointed outhereinbefore, the coloring agent may be added during mixing of theingre-clients of the powder components or after the powder componentshave been prepared.

The granular casting powder and burning rate control powder are mixed orblended in any suitable manner such as, for example, in a sweetie barreland introduced at an even rate into the casting container. If theburning rate control powder is in the form of strands or filaments,these are anchored in spaced relation by upper and lower perforateddiscs, placed in the casting container, and casting powder poured inaround them. A weighted member is then placed on the powder column tohold the granules in place during subsequent operations.

The casting container is formed of a nonammable, transparent material toinhibit burning of the cast propellant and to permit inspection of thepowder components after they have been introduced into the container.Preferred materials of this type are those which can be plasticized bythe casting solvents, so as to secure a strong bond between the powderand container. An example of such preferred material is celluloseacetate.

The nonvolatile plasticizers or casting solvent are preferably admittedto the container or mold through an opening in its bottom portion andforced upwardly through the powder column under a pressure head createdby raising the liquid level of the plasticizer several feet above thetop of the mold. Any other means such as pumps, reduced pressure insidethe mold, etc., could be used procided the introduction of the liquid isaccomplished at the desired steady rate. The rate at which theplasticizer rises in the mold will desirably be as great as possiblewithout entrapping air in the powder column. Upward displacementsvarying from about 5 to about 10 inches per minute are preferred,although rates as high as 20 inches per minute may be used especiallywith larger powder granules and less viscous plasticizers than thosecited in the example. The opening for admitting the plasticizer may beof any suitable size and is located in any portion of the bottom of themold. Preferably, the size of the opening will be from about 1/s inch toabout 1 inch and centrally located.

After the plasticizer has been introduced, the weight on top of thepowder column is removed and the container with contents placed in -aheated atmosphere to cure. Curing is desirably accomplished by placingthe casting in a forced air oven for a period from about 1 hour to about600 hours and at a temperature from about 30 C. to about C., andpreferably for about 40 hours at 60 C. It Will be realized, -of course,that any suitable type of drying and/ or curing device may be used andthat temperatures and times may be adjusted and coordinated byprinciples well known in the art.

The device of the present invention can be used in any compositesmokeless powder charge or load, in which the arrangement ordistribution of the component powder particles must yfollow aprearranged order. It has widest application to the manufacture of castpropellants for use in rockets, assisted takeoff motors, and otherjet-controlled uses.

The present invention provides a quick, easy, and inexpensive way toinsure that the powder components are properly arranged through thecasting. By inspecting the castings just before the plasticizers areadded, it is possible to recover and reuse the powder and plastic moldcomponents of faulty castings, simply by pouring the powder back intothe blending barrels, and relling the molds. Finished castings maylikewise be examined and faulty distribution detected. As a result,faulty castings giving irregular burning with consequent hazards andundependability in use, are eliminated.

What I claim and desire to protect by Letters Patent is:

1. In the manufacture of cast smokeless powder propellents from amixture of powder ingredients, the method which comprises forming thepowder components with distinctly different colors, mixing the powdercomponents so as to obtain a uniform color pattern indicative of thehomogeneity of the powder, introducing a mixture into a transparentcontainer to form a charge, introducing a casting solvent through anopening in the bottom of said transparent container and curing thecontents of said container at an elevated temperature to form a casting.

2. A method in accordance with claim 1 in which the distinctly differentcolors are obtained by the addition of coloring agents to the powdercomponents during formulation thereof.

3. A method in accordance with claim 1 in which the distinctly differentcolors are obtained by the addition of coloring agents to the powdercomponents after formulation thereof.

4. A method in accordance with claim 1 in which the distinctly differentcolors are obtained by coating the powder components.

5. A method in accordance with claim 1 in which the distinctly differentcolors are obtained by the addition of inorganic pigments to the powdercomponents.

6. A method in accordance with claim 1 in which the distinctly`diiierent colors are obtained by the addition of organic pigments tothe powder components.

7. In the manufacture of cast smokeless powder propellents from powdercomponents including a casting powder, a burning rate powder and acasting solvent, the method which comprises forming the powdercomponents with distinctly ditferent colors, mixing the casting powderand the burning rate control powder so as to obtain a uniform colorpattern indicative of the homogeneity of the powder, introducing themixture into a transparent container to form a charge, introducing acasting solvent through an opening in the bottom 0f said transparentcontainer and curing the contents of said container at an elevatedtemperature to form a casting.

8. In the manufacture of cast smokeless powder propellents from amixture of powder components and a casting solvent, the method whichcomprises coloring the powder components with coloring agents producingdistinctly dilferent colors, at least one of said coloring agents beingtitanium dioxide, mixing the powder components so as to obtain a uniformcolor pattern indicative of the homogeneity -of the powder, introducingthe mixture into a transparent container to form a charge, introducingthe casting solvent through an opening in the bottom of said transparentcontainer and curing the contents of said container at an elevatedtemperature to form a casting.

9. In the manufacture of cast smokeless powder propellents from amixture of powder components and a casting solvent the method whichcomprises coloring the powder components with coloring agents producingdistinctly different colors, at least one of said coloring agents beingcarbon black, mixing the powder components so as Vto Vobtain a uniformcolor pattern indicative of the homogeneity of the powder, introducingthe mixture into a transparent container to form a charge, introducingthe casting solvent through an opening in the bottom of said transparentcontainer and curing the contents of said container at an elevatedtemperature to fonm a casting.

10. In the manufacture of cast smokeless powder propellents from amixture of powder components and a casting solvent the method whichcomprises coloring the powder components with coloring agents producingdistinctly different colors, at least one of said coloring agents beingpara red, mixing the powder components so as to obtain a uniform colorpattern indicative of the homogeneity of the powder, introducing themixture into a transparent container to form a charge, introducing thecasting solvent through an opening in the bottom of said transparentcontainer and curing the contents of said container at an elevatedtemperature to form a casting.

References Cited by the Examiner UNITED STATES PATENTS 1,605,655 11/1926Du Pont 102-42 2,353,934 7/1934 Schreib 102-38 2,417,090 3/ 1947 Silk etal. 520.5 X 2,440,327 4/ 1948 Crawford. 2,574,479 11/ 1951 Hickman.2,643,611 6/1953 Ball 52-O.5 X

FOREIGN PATENTS 21,240 1906 Great Britain.

LEON D, ROSDOL, Primary Examiner.

ALEXANDER BISHOFF, WILLIAM G. WILES,

ROGER L. CAMPBELL, Examiners.

L. H. MYERS, A. P. KENT, W. A. KEMMEL,

Assistant Examiners.

1. IN THE MANUFACTURE OF CAST SMOKELESS POWDER PROPELLENTS FROM AMIXTURE OF POWDER INGREDIENTS, THE METHOD WHICH COMPRISES FORMING THEPOWDER COMPONENTS WITH DISTINCTLY DIFFERENT COLORS, MIXING THE POWDERCOMPONENTS SO AS TO OBTAIN A UNIFORM COLOR PATTERN INDICATIVE OF THEHOMOGENEITY OF THE POWDER, INTRODUCING A MIXTURE INTO A TRANSPARENTCONTAINER TO FORM A CHARGE, INTRODUCING A CASTING SOLVENT THROUGH ANOPENING IN THE BOTTOM OF SAID TRANSPARENT CONTAINER AND CURING THECONTENTS OF SAID CONTAINER AT AN ELEVATED TEMPERATURE TO FORM A CASTING.